1. Field of the Invention
This invention relates to respiratory devices and, more particularly, to endotracheal tubes that are adapted to be inserted down a patient's trachea and to provide air to a patient's lungs.
2. Description of the Related Art
Endotracheal tubes are used to ventilate a patient by forcing air into the patient's lungs. Exhalation naturally follows. Ventilation is necessary, for example, during surgery, after lung failure, or to assist anyone who is having difficulty breathing. An endotracheal tube is an elongated tube that is inserted into the patient's throat and down into the patient's trachea, or windpipe. For easier insertion and reduced chances of tissue damage, the diameter of the tube is somewhat less than the natural diameter of a typical throat. The length of the endotracheal tube is such that the proximal end of the tube is located in the patient's mouth and can be connected to an air supply or breathing apparatus, while the distal end of the tube is located in the patient's trachea, past the vocal cords. During ventilation, air is forced into the open proximal end, down the tube, out the open distal end, and into the patient's lungs. During exhalation, air is allowed to leave the patient's lungs and travel back up the tube.
For effective ventilation, the air forced down the endotracheal tube must enter the lungs with minimal loss of escaping air. Therefore, the air must be blocked from escaping around the open distal end of the tube and flowing back up the patient's trachea in the space between the endotracheal tube and the trachea. Because of the need to block the air, an endotracheal tube is provided with an inflatable cuff that is usually located near the tube's distal end, past the vocal cords. When the distal end of the tube is being inserted down into the patient's trachea, the cuff is maintained in a deflated condition, for easier passage. Thereafter, he cuff is inflated until it presses against, and occludes, the trachea, to prevent the air that leaves the open distal end of the tube from flowing back up the trachea. Rather, the air is forced out the tube's open end, down the remainder of the trachea, and into the patient's lungs. A separate inflation tube that communicates with the cuff is provided along the length of the endotracheal tube. Inflation and deflation of the cuff is controlled by an air valve at the proximal end of the inflation tube.
A serious drawback to using endotracheal tubes is that the inflated cuff causes damage to the soft tissues of the trachea. The tissue damage is believed to be at least partially a result of a reduced blood flow to the soft tissues that follows from inflation of the cuff. Scar tissue can form in the trachea past the vocal cords, which is a condition known as subglottic stenosis. This is a very difficult problem to treat and can require the placement of a tracheostomy tube in the patient, often for the remainder of the patient's lifetime. Unfortunately, ventilation with the endotracheal tube requires the cuff to be inflated.
Studies have indicated that even relatively short periods of cuff inflation can cause damage to the soft tissues. As a result, a patient cannot physically tolerate intubation with an inflated cuff for extensive periods of time, and damage can occur after intubation during relatively short surgeries. Patients often have improved resistance to tissue damage if the cuff is periodically deflated during extended periods of intubation, but under many circumstances, such as surgery, periodic deflation might not be possible. At the very least, it is very inconvenient to constantly inflate and deflate the cuff when using the endotracheal tube, and the tube is often used under circumstances where having to keep track of inflation and deflation is impractical.
From the discussion above, it should be apparent that there is a need for a respiratory device that can be used to ventilate a patient for extended periods of time, without causing damage to the soft tissues of the trachea. The present invention satisfies this need.